Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

182
FXUS63 KLOT 161951
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
251 PM CDT Thu Apr 16 2026

.KEY MESSAGES...

- Dense fog is possible tonight, especially closer to Lake
  Michigan.

- Another round of showers and thunderstorms is expected later
  Friday afternoon into Friday night. Some of the storms could
  be severe. Locally heavy rainfall could result in flooding
  issues.

- Windy and unseasonably warm weather Friday will be replaced by
  much colder weather over the weekend into early next week.

- Frost/freeze conditions are expected many areas Sunday and
  especially Monday mornings.

&&

.DISCUSSION...
Issued at 251 PM CDT Thu Apr 16 2026

Through Friday night...

Surface ridge will move across the region tonight. Relatively
moist low level air mass remains in place, so as skies clear
out and winds diminish, areas of dense fog could develop
tonight. The threat appears greatest near and downwind from Lake
Michigan as marine chilled air mass bleeds inland into higher
dewpoint air mass over land. May very well need a dense fog
advisory tonight, but will punt that decision to the evening
shift who will benefit from observational trends and be able to
better define the areas of greatest dense fog threat.

Friday will be the last summer-like warm and windy day of this
stretch, out ahead of an elongated surface low lifting towards
western Lake Superior. Expect highs in the low to locally mid
80s away from the far northeast IL shore (which will reach the
70s towards evening), and southerly winds gusting up to 30-35
mph. Lingering lower dew points from underneath the departing
surface high, south-southeast winds to offset surface moisture
return with eastward extent, and parched mid-levels will yield a
fairly sharp instability gradient from the MS River to the
longitude of Lake Michigan by mid Friday afternoon.

Significant uncertainties remain regarding severe weather threat
in our CWA late Friday and Friday night. A number of high
resolutions models are developing open warm sector convection
across western IL by mid afternoon Friday. It isn`t clear what
is forcing this convection, which given the stout EML and
potential for a cap, raises doubts about the veracity of the
model solutions depicting this. Are these models too aggressive
in eroding convective inhibition in light of the strong EML? It
really isn`t clear at this point, leading to lower forecast
confidence in the afternoon.

Should this convection develop in the open warm sector during
the afternoon, then storm mode would likely be supercellular
given the long hodographs. Primary threat from these storms (if
they materialize) would likely be large to very large hail.
Cannot rule out a tornado threat, however low level shear looks
fairly marginal. In addition, it isn`t clear how much dewpoints
will mix out and even modest mixing out of low level moisture
would lead to larger T/Td spreads and a more muted tornado risk.

Regardless of whether this open warm sector convection
materializes, an extensive frontal squall line is likely to
develop west of the Mississippi River along the approaching cold
front. Given the parameter space this convection will develop
within, severe weather is likely, especially damaging winds.
This QLCS should cross the MS River and move into our western
CWA early-mid evening Friday. This line will likely still pose a
threat of damaging winds and potentially line embedded
tornadoes given the strengthening low level shear during the
evening.

Lower confidence in how quickly the convection will decrease in
intensity as it moves east across our CWA into less unstable and
more capped air mass. The latest SPC SWODY2 nicely depicts the
likely west to east gradient in severe weather threat.

There is a pretty strong signal in guidance in a southern stream
shortwave slowing the southward progression of the extensive
QLCS across central IL Friday night. In fact, there could be a
reinvigoration of convection capable of producing heavy rainfall
in association with this wave. The southern portions of our CWA
seem most susceptible to a more prolonged period of heavy
rainfall Friday night.

Soils are saturated and streamflow much above average over much
of the region, leaving our CWA susceptible to both flash
flooding and river flooding from heavy rainfall. Our WI border
counties and the immediate Chicago area are most vulnerable to
flooding, and should heavy rain fall in these areas, then a
more significant flood threat would exist. Have issued an ESF to
highlight this threat for now, but once we are better able to
define the areas most likely to potentially see heavy rainfall a
flood watch will likely be needed.

- Izzi

Saturday through Wednesday:

The most recent model guidance for Saturday has pretty
unanimously sped up the timing of the cold frontal passage to
yield a mostly dry day for much of if not the entire area. Best
chance (30-50%) for any lingering showers past sunrise will be
for areas southeast of I-55. Saturday afternoon will trend to
partly cloudy to mostly sunny, albeit notably cooler (50s) with
blustery west-northwest winds. Cold air advection and dry
advection through Saturday night-early Sunday will set the stage
for lows in the 30s, possibly flirting with freezing across
parts of interior northern IL. Following a cool and breezy
Sunday, ~1030 mb high pressure over the region will likely be
conducive to at least areas of frost as temps dip to the low-mid
30s outside of Chicago, if not colder in spots. Agricultural
interests are advised to monitor forecasts through early next
week.

Cooler conditions into Monday morning will be short-lived
however, with extended guidance favoring a return to high
amplitude ridging across the central CONUS and unseasonably warm
temperatures returning to the region by midweek next week.
Despite the returning warmth next week away from Lake Michigan,
a blocky mid-upper pattern will favor much less stormy
conditions over the local area, giving a longer period to dry
out from this week`s rain.

Castro


&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1233 PM CDT Thu Apr 16 2026

Key Messages:

- A few VCTS expected early this afternoon, particularly across
  the main Chicago area terminals.

- Easterly wind shift with lake breeze either late this
  afternoon or early this evening.

- Fog/low CIGs likely to shift in off the lake this evening and
  tonight. Potential exists for LIFR to VLIFR conditions are
  the Chicago area terminals overnight.

A weather disturbance, currently shifting overhead across the
northeastern IL terminals, is fostering a few lines of showers
and thunderstorms early this afternoon. While these will be
around the terminals through around 19Z, the main focus for
these is expected to expected to gradually slide east-
southeastward through the afternoon. However, a few additional
isolated showers and storms could develop overhead in the wake
of this activity. Should any additional showers develop, their
coverage should remain low and largely hit or miss.

Otherwise, breezy westerly winds this afternoon will shift
east- northeasterly by early this evening as a lake breeze
pushes inland across the Chicago area terminals. Thereafter,
concerns will reside around the increasing potential for fog
and very low CIGs to move in off of Lake Michigan this evening
and tonight. Accordingly, we have opted to hit the VSBYs and
CIGs harder with the morning update, particularly for the main
Chicago area terminals. Admittedly, however, conditions could
be even be lower than what is currently highlighted in the TAFs
for a period tonight. Conditions should then improve by mid-
morning on Friday as the surface flow begins to increase and
become gusty from the south-southeast.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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